Sterilizing materials and methods for making the same



Patented Mar. 12,1946

STERILIZING MATERIALS AND METHODS FOR MAKING THE SAME Ignaz Kreidl and Werner Kreidl, New York, N. Y., assignors to Ludwig Jekels, New York, John Heller, Hartsdale, N. Y., and Ignaz Kreidl, and

Werner Kreidl, both of New York, N. Y.

No Drawing. Application March 20, 1943, Serial No. 479,957

9 Claims. (Cl. 167-14) This invention relates to disinfectant products and to methods for making the same. More particularly it relates to disinfectant products which contain silver in combination with halo- 6 those of chlorine and bromine, since the solu- The specific action of silver and its compounds bility of silver iodide is much lower'than that with respect to living organisms and, accordingly, of the other silver halides, in consequence whereits antiseptic, disinfectant and the like action of its disinfectant power may not be satisfactory is well known in the art, especially colloidal for certain fields of application. preparations of silver and silver oxide have been 10 Although the theory of the action of the exsuggested for therapeutic and the like purposes. cess halide is not quite understood, and the ac- It also has been suggested to introduce elemental tual molecular structure of such combination silver or silver chloride into aqueous media by P s do not form part of this invention, it means of electrolysis. Most of those known silmay be assumed t t t e S lver halide products. ver preparations are difficult to prepar h v according to this invention owe their increased an undesirable dark color and are none too s ty o a c p formation of the simple stable with respect to organic matter and light. Silver halide 8 with Other l- An object of this invention is a disinfectant d It a pears that in thi protested s t product having silver halide in a stabilized form the Silver s more tightly bound to the ge asthe efiective agent. Another object is a relaand thus not readily reduced by the solarizing tiv ly insoluble, stable silver halide disinfectinfluence of light. Re a d ess f a y possible ant. Another object is methods for preparing theory, our invention m y e o e c early esuch disinfectants. Another object is disinfectfi y e actual methods f y n it Out ant silver halide solutions containing more silver and by t esc p on of he P ucts resultin halide than corresponds to the solubility of the t e fro simple silver halide. Another object is methods AS has been mentioned above, the Stability of for making such solutions. Another object is a e Silver p at ns cord g to this invendisinfectant material being impregnated with tion is caused by the Presence f n x ss of such stabilized silver halide compositions. Anhalides or substances of the halide typey a other object is methods for making such imsubstance of the halide type a halogen compregnated disinfectant materials. Further obpound is to be understood, which, according to jects will become apparent in the following deits basic formula, has an anionic Cl p. scription. group, or I group and, accordingly, may be a This invention is a continuation in part of our derivative of the corresponding halide acids or application S. N. 429,956 of February 2, 1942 for may be such an acid itself, however, disregardan improvement in Sterile products and procing the fact whether or notin the particular esses for preparing the same. combination it is bound in complex form. Thus,

This invention is based on'the discovery that for example, if the basic formula of the comdisinfectant silver halide preparations of an in- 40 pound would be Ag.Hal.(Hal.M)e substantially creased stability, more particularly with respect all of the halogen can be allotted to compounds towards the action of light, may be obtained by of the general type M.Hal or M.Hal although having the silver halide protected by an excess actually some of the halides may be bound in of halide. Within the scope of this invention complex form, such as in a halogeno compound: term halide is understood to comprise the de- AgI-lalz'M. The term halogeno compound, as rivatives of chlorine, bromine, and iodine, while used here, refers to a type of theoretical comfluorine compounds are not included since the pounds which sometimes are referred to under fluorine compounds of silver diifer greatly from this name, and which correspond to the general those of the other halogens, both with respect formula: AgHaleM, where Hal is chlorine, broto their physical properties, such as solubility mine, or iodine and a: a number between 1 and 4,

and stability to light, as well as with respect to their chemical properties. As far as solid preparations are concerned, iodine compounds,'.i for many purposes, will not be quite as efiective as and M the stoichiometric amount of a cation. including hydrogen.

According to one modification of our invention, stable solutions of the silver halides of chlorine, bromine and iodine which are highly suitable for disinfectant and the like purposes, but which are also of advantage for the preparation of solid silver halide preparations of limited solubility, as will be discussed more in detail in later parts of this specification, may be obtained by having the silver halides in solution in the presence of an excess of halide in the form of soluble halides of the halogen acids of chlorine, bromine and iodine, or in the form of the halide acids themselves. Without restricting this invention to any theory it may be assumed that the stability of such solutions may be due to the formation of complex silver halide compounds as described above. It need not be mentioned that not all of the excess halide will or need participate in the said complex formation, but, as appears to be witnessed by the increased solubility of the silver halides in more concentrated halide solutions, the formation of complex-like silver halides seems to be favored by increasing concentration of the halide type compounds. It was found, and this forms an important part of our invention, that such stable soluble silver halide compounds will not coagulate proteins and thus will not have any of the undesirable properties of the hitherto known silver disinfectants or other protein coagulating antiseptics. This property of the silver halide solutions according to this invention renders them particularly useful where they are to be used for bacteriostatic action in the treatment of the human body.

In preparing solutions according to the present invention the silver may be introduced in any convenient form, preferably, however, in the form of a readily soluble silver salt, such as silver nitrate, silver acetate, or silver sulfate and the like. Wherever the introduction of anions other than halide is undesired, the silver may be introduced in the form of the not readily soluble simple silver halides of chlorine, bromine, and iodine or in the form of its oxide. However, in this case solution will be greatly aided by the application of heat. The excess halide may be introduced in the form of any halide capable of bringing into solutions more of the simple silver halide than corresponds to its solubility. Thus, for example, the halogen acids of chlorine, bromine and iodine may be used. By way of example the following soluble halides of these acids may be named: alkali metal, alkali earth metal, aluminum, copper, bismuth, lead and cerium chlorides, bromides and iodides. In certain cases, the use of halides in amounts where the cation may be capable of forming complexes, such as excess ammonia, will not be desirable since the effectiveness for certain uses may be impaired.

Generally speaking, and especially where such silver preparations are to be used for the treatment of the human body, or in'connection with foodstuffs or other materials for human consumption. the use of alkali halides for the introduction of excess halide will be preferable, due to their neutral and non-poisonous character, such as, especially, common salt. Also, the non-poisonous alkali earth metal halides; that is, calcium, and magnesium chloride will be advantageous, the high solubility of calcium chloride offering further advantages as will be seen later on.

For dissolving each given amount of silver a certain amount of halide will be necessary, and the maximum amount of silver which may be dissolved will be dependent on the maximum amount of the halide which may be dissolved in the solution. No definite rules for determining the amount of silver which can be brought into solution by a given amount of halide can be established theoretically, but this amount can be easily determined by simple experiment. Generally speaking, for any increases in the concentration of the halogen furnishing compound, the concentration of silver which can be brought into solution will increase at a much greater rate. Roughly speaking, solutions containing the same amount of the various halogens will dissolve approximately the same amount of silver.

It was found that the effectiveness of such silver halide solutions may be improved for many purposes if they are allowed to act in an acid medium, preferably a slightly acid medium. As a matter of fact, the effectiveness of solid silver halide preparations according to this invention may also be improved if they are used in contact with acid or slightly acid media. For this purpose also acids other than halogen acids, if compatible with the silver halides, may be used. By slightly acid, as is well understood by those skilled in the art, we mean acidities between neutrality and about pH 3, preferably closer to about pH 3, without, however, restricting the inventions to any particular pH. i The selection of a suitable pH will largely depend on the actual use of the preparation. Other acidities will be desirable in the treatment of wounds as in the preservation of foodstuffs, while in other fields of application the selection of any particular pH may be of slight value only.

Accordingly, the present invention offers a means for providing silver solutions having a relatively high silver concentration and which are stable to light and do not readily react with organic matter. Such solutions may be used with great advantage for the disinfection, sterilization, therapeutic or antiseptic treatment, fungicidal, insecticidal, bactericidal treatment and similar treatments of a great variety of objects such as of surgical instruments, sanitary containers, containers for pharmaceutical or foodstuff products or other perishable goods and for any other purpose for which the bacteriological or the like action of silver may be effectively used. Such solutions are especially effective or advantageous where they may come in contact with metals since the silver will not be P ecipitated therefrom on such contact. Such solutions, especially those concentrated in silver, that is, solutions which are saturated with respect to silver, or have concentrations close to saturation,

however. cannot be used indiscriminately wherever they can come into contact with water, or aqueous solutions, or moist materials, since they may be easily precipitated. The preparation of solutions and solid preparations of a predetermined solubility do not form subject of this invention, but of our copending application of same date, S. N. 479,959 of March 20, 1943, for improvement in sterilizing products and making the same. Preferably, therefore, the solutions according to the present invention will be used for the treatment of dry products, such as for dry solid materials or in the preparation of solid, slightly soluble products as will be discussed more in detail in the following. However, their use is by no means restricted to such application and in many cases the formation of such a precipitate in contact with moist or liquid materials will be desirable. Thus for example, such solutions which will precipitate on contact with water or aqueous liquids may be used with advantage in the treatment of wounds or infected dental cavities since a highly efiective silver halide preparation of only slight solubility will be precipitated directly on the surface to be treated, and thus provide a more or less permanently active protection or disinfecting action on the surface thus treated. Precipitation from such solutions will always occur where the excess of halide over the silver halide is not carefully adjusted. However, the present invention contemplates such solutions broadly, while special adjustment of the ratio of halogen to silver forms subject of the above mentioned copending application.

According to another modification of ,our invention solid disinfectant silver halide preparations may be prepared which are only slightly soluble and, accordingly, at any given time will give ofi only small, though effective, amounts of the active silver and, accordingly will have a more or less permanent disinfecting property. Such solid products, according to our invention, will be characterized by the fact that they contain more halogen than corresponds to the stoichiometric composition of the simple silver halide (AgCl, AgBr, AgI) the excess halogen being present in the form of a halide type compound of chlorine, bromine, and iodine, the excess halogen, however, being not great enough as to increase the solubility of the formed stabilized compound substantially over that of the simple silver halide or that of the theoretical halogen compounds. The stability of such solid slightly soluble silver halide preparations according to this invention will be greatly increased by having them truly adsorbed on carrier such as on natural vegetable fibres, such as cotton fibres, or on adsorbent minerals, such as clays, and other adsorbent silicates and aluminum compounds. It is believed, although the invention is not limited by the theory, that the adsorption forces have a similar favorable effect on the stability of the solid, slightly soluble silver preparations, according to our invention, as the much greater excess of halides in the case of our liquid preparations. The increased stability of such adsorbed silver halide products is evidenced by the fact that only such adsorbed silver halide products of a slightly soluble character are not split by water but will give ofi gradually small amounts of the silver halide compound to a solvent without being affected by their light stability.

Such solid disinfectant or the like silver halide adsorption products may be prepared by any number of processes and methods, provided that their final composition is in accordance with the characterization as given above. Whatever method for adsorbing such products on a carrier is used, always care has to be taken that any not adsorbed silver halide is removed since such nonadsorbed silver halide may not be stable to light.

Of course such an excess of non-adsorbed silver halide need not affect the efiiciency of the impregnated material, but it may greatly impair its appearance. Curiously enough the same solutions may be used as impregnation baths as are described in the preceding sections and in the above mentioned copending application in connection with dilutable, but not infinitely dilutable, silver halide solution or readily soluble impregnations. The insolubility of the impregnation according to the modification disclosed in this section is obtained by the adjustment of the halogen to silver ion ratio of the adsorbed product. In practically all cases this adjustment is simple enough, since most carriers, such as cotton, will not truly adsorb large enough an excess of halide as to increase the solubility of the adsorbed product substantially over that of the simple silver halide. As a matter of fact, it may be assumed, without restricting our invention to this theory, that the effective excess halide i not directly adsorbed by the carrier but by the silver halide. Accordingly, in order to obtain such a product, which will be stable to light and only slightly soluble it will be necessary either to adsorb on the carrier just the required amount of silver and halide or if the impregnation has been carried out with an excess of material to remove all the not truly adsorbed excess.

Generally'speaking one may distinguish between two types of impregnation which may be utilized in the preparation of such slightly soluble, adsorbed silver halide products. Either the impregnation may be carried out in two stages, that is, first with one reactant and then with the other one, preferablyfirst with a silver salt and then with a halide type compound, or the impregnation may be made from a solution of a silver halide product as described in earlier parts of this specification or in the above mentioned copending application. 7

In using a process for impregnation in two stages the carrier, for example, a bandage gauze, may be first soaked in a silver nitrate solution. The thus treated gauze then preferably will be dried. As a rule, for a standard bandage gauze not more than about 4% silver nitrate should be retained on the fiber sincegreater amounts will not lead to truly adsorbed products. The gauze then may be dipped into a suitable halide solution, such as into a sodium chloride solution. The completeness of the ensuing reaction will be dependent on the time, temperature and concentrations used. Higher temperature and/or concentration will reduce the time necessary for complete reaction, However, too high a halogen concentration or too large a halogen amount may keep too much silver in solution. After the reaction is completed the gauze has to be washed so as to remove any non-adsorbed salts, regardless of the fact whether they are soluble or precipitated. For example, when having about 1% silver nitrate retained on the fibers of such a bandage gauze a cold treatment in a 20% sodium chloride solution for one hour or in a 5% solution for twenty-four hours will give good results. Alternatively, the silver salt with which the gauze or the like has been soaked may be reacted with a halide solution which is saturated with respect to silver by which expedient any loss in silver from the gauze is avoidable.

When adsorption is effected from any of the earlier described solutions, or those described in the copending application, but not infinitely dilutable solutions, containing silver and an excess halide the carrier may be simply dipped into such a solution and then precipitated with water. Excess non-adsorbed silver halide compounds which just adhere to the fibers then have to be washed fiifhcarerully, because they will not be stable to t. Preferably, however, the impregnation in one stage is carried out in accordance with the rules outlined in the following. It wasfound, and this forms an important part of our invention, that adsorbent materials. such as cotton, when in contact with a solution containing silver and excess halide will preferably adsorb silver ions and thus deplete the impregnation bath in silver at a much greater rate than in halide ions. Accordingly, the concentration of silver as computed for the amount of liquid retained on the carrier will be much greater than in the impregnation bath. It was furthermore found that this property can be utilized for impregnation of the adsorbent carrier to great advantage, if the liquid adhering to the carrier is removed therefrom under conditions which will prevent precipitation of the silver contained therein. Without restricting our invention thereto the following means for removing the adhering silver halide without precipitation may be mentioned:

a. A bath of such a low silver concentration is used that after adsorption concentration is lowered to the true solubility of the simple silver halide.

b. A bath is used that after adsorption the halogen to silver ion ratio corresponds to that of an infinitely dilutable solution or of suitably predetermined dilutability according to the rules in the above mentioned copending application or predeterminedly dilutable solution to start with.

c. The ratio is adjusted according to b but for washing in hot water.

d. Washing with halide containing .water, the amount of halide being adjusted to Just keep in solution the adhering non-adsorbed silver halide compounds.

With the exception of the method given under a this modification of our invention may also be used, especially for continuous impregnation, with baths which are permanently replenished from a solid silver compound such as solid silver halide in a solution saturated for silver thiocyanate, which is in contact with the bath.

The halogen to silver ion ratio for any predetermined dilutability according to the above mentioned copending application can be easily determined by experiment. The theoretical halogen to silver ion ratio preventing precipitation for any specified dilution may be easily determined by experiment. For determining this ratio it will be only necesary to determine the amount of halogen necessary to keep in solution the amount of silver which is to be kept in solution at the required maximum dilution, provided that this amount of silver is well above the true solubility of the simple silver halide. Accordingly, to find the theoretical halogen to silver ion ratio for such a silver halide preparation which can be diluted without precipitation to any desired degree and down to infinity it will be necessary only to determine the minimum amount of halogen necessary to dissolve the first measurable increase in the silver concentration over the amount soluble in the form of the simple silver halide in pure water. The ratio of this amount of halogen to the excess silver over that introducible as the simple silver halogen will give the required theoretical ratio. The maximum silver concentration of such a dilutable solution will be determined by the maximum amoimt of halogen which can be introduced into it, a factor which will largely depend on the specific compound used. Where not infinite dilutability but only dilution to a certain predetermined silver concentration is desired the theoretical halogen ion to silver ion ratio may be determined in exactly the same way by determining the amount of halogen necessary to keep the desired silver concentration dissolved at the predetermined maximum dilution. Thus, for example. if such a silver halide preparation should be capable of standing dilution without precipitation until a is the silver concentration of the diluted preparation and it is found that at this dilution 1! is the concentration of halogen ions necessary to keep the silver in solution, halogen to the silver ratio for the concentrated solution will be yzz. If the concentrated solution can dissolve 2 times as much halogen ions as are necessary to keep the silver dissolved in the diluted solution it can be seen that the most concentrated stock solution which can be prepared for this halogen silver ion ratio will contain 2 times 1/ halogen ions and 2 times a: silver ions. In some cases it will be desirable to adjust the required ratio to a certain halogen concentration in the diluted solution. In such cases all one has to do is, of course, to reverse the above procedure.

Actually lower ratios than those determined by the above theoretical considerations can be used and as a rule, particularly for solutions having not too high a halogen concentration about a fifth to a tenth of the theoretical ratio can be safely used, most likely due to the fact that on dilution a certain supersaturation for silver can be attained. Thus, for example, an infinitely dilutable solution may beprepared from a solution having a chlorine to silver ion ratio of about 1200, while the theoretical value would be about 6000 to 10,000. The required practical ratio for any desired dilutability may be easily determined by experiment.

The approximate ratio for infinite dilutability as well as the theoretical dilutability as given in the preceding paragraphs applies to aqueous solutions at room temperature only. The solubility of silver in halide ion containing solutions, however is dependent on the temperature to quite some degree. It will be understood readily, that, accordingly, for temperatures deviating from room temperature the useful halogen silver ratios will have to change in. accordance with the change in solubility. It need not be explained in detail that for any given temperature above and below room temperature, the required ratios for infinite and limited dilutability can be easily determined.

The temperature eil'ect on solubility can also be utilized in another way. Change in temperature as a rule also influences the solubility of the halide introducing compounds and as usual an increase in temperature will increase the solubility of such compounds.

In this connection, as well as throughout the specification and the appended claims the term halogen ions" is to be understood as designating anionic halogen, regardless of the fact whether it is in the ionized state or not. The same applies to the term "silver ions."

In applying the above general methods or analogous methods the following rules and conditions will be helpful and teach how to select the best conditions for any given requirements.

1. Adsorption should be effected from solutions I containing not more than one-half, preferably about one-fifth to one-tenth, of the absolute amount of silver which is to be adsorbed on the carrier.

2. The halide content of -the bath should not greatly exceed the amount necessary to keep the silver in solution.

3. From a bath containing no solid silver to replenish it the adsorbent carrier will adsorb silver selectively until a minimum content of silver is reached at which the bath may be designated as exhausted withrespect to the given carrier.

4. The higher the halide content of the bath or the hotter the bath the higher will be the silver content of the exhausted bath.

5. Adsorption is favored by increased temperature and/or silver content of the bath.

6. Complete adsorption is not a momentaneous,

but a time reaction, whereby factors reducing the time for adsorption increase, which is sometimes undesirable, the concentration of silver of the exhausted bath.

For any practical application of the above methods and rulessuch conditions will be selected which appear most suitable for the purpose in mind. Under favorable conditions the silver retained on the carrier when computing it as weight percent of the carrier may be about ten times as high as in the solution. This will be especially the case where the halogen concentration of the bath is very low, such as about one percent only. The absolute amount retained on the carrier will be influenced by a number of conditions. Increased halogen content of the bath favors adsorption, but increases the silver content of the exhausted bath, accordingly to make use of this increased adsorption the absolute content of the bath has to be increased at an accordingly greater rate than the halide content. Thus, for example, the composition of the bath for a given amount of the carrier may be determined as follows. First one determines for a given amount of bath the silver content retained on exhaustion" for a given halide concentration. After this determination one can predetermine any desired impregnation within limits for the carrier, the upper limit being given by the maximum adsorption of which the carrier is capable or by the saturation in silver for the given halogen concentration, by dissolving just as much silver in the bath as is to be adsorbed by the carrier. More impregnation is made from a bath the silver content of which is continuously replenished by being in contact with excess silver in a bath which is saturated for silver the amount of silver which will be adsorbed by the carrier may also be influenced by the time for which the carrier will be in contact with the bath.

It was found that such slightly soluble, solid, adsorbed silver halide preparations may coagulate protein, which will be particularly undesirable in the treatment of wounds. It was found that this can be prevented by certain impregnations or additions. It was found that substances capable of forming complexes with silver are suitable for.

above mentioned copendin-g application may be used for this purpose. In practical application on the carrier impregnated with the slightly soluble, adsorbed silver halide preparation would, for example, be impregnated with such a soluble substance prior to its being brought into contact with a wound or the like.

It may be mentioned that in all methods which depend on the adsorption of the silver halide preparation the nature of the adsorbent material will be of importance, If sized or raw fibers, which still retain their natural vegetable fats, are impregnated it must be kept in mind that, according to the nature of the sizing or the oils and fats, they may favorably or unfavorably influence the adsorption. It is quite obvious, on the other hand, that materials, which by nature are nonadsorbent for the disinfectant silver halide preparations according to this invention, may be treated so as to become adsorbent therefor.

However, no particular method for making such rial for preparing materials according to this invention, Also in the case of the preparation of such solid, slightly soluble silver halide preparations it will be of no importance what silver or halide compounds are used as starting materials. As a rule it will be most convenient to prepare them by reacting in solution a soluble silver salt and a soluble halide. If desired, however, such products may be prepared directly by reacting the insoluble simple silver halides of chlorine, bromine, or iodine with a solution of the excess halide. In many cases it may be advantageous to prepare such solid slightly soluble silver halide preparation with a hygroscopic character. In order to obtain such products hygroscopic halides, such as more particularly calcium chloride, will be used as the excess halide.

The present invention may be illustrated by the following examples: I

Example 1.A bandage gauze is impregnated with a 2% silver nitrate solution and wrung so as to retain 4% by dry weight silver nitrate. The thus impregnated gauze is dried and then boiled for one hour, in a solution containing 5%. sodium chloride. The thus treated gauze is washed.

Instead of a 5% sodium chloride solution a 5% sodium bromide solution may be used or a 3% sodium chloride or bromide solution containing 1% hydrochloric or hydrobromic acid may be used.

The sodium chloride solution may be furthermore replaced by a calcium chloride, aluminum chloride or cerium chloride solution or by any of these solutions in combination with hydrochloric acid.

Example 2.391 parts water are mixed with 412 parts of anhydrous calcium chloride and 18 parts silver nitrate and boiled until a clear solution is obtained.

Gauzes, natural and synthetic sponges, may be impregnated with this boiling solution or boiled with it for up to one hour preferable so that the material will contain 300% by weight of the said solution, if possible. The thus impregnated product will be dried and then washed and then dried again.

The above solution may also contain 1 to hydrochloric acid.

Example 3.A solution is prepared containing 34.5% calcium chloride and .85% silver nitrate and if desired 1 hydrochloric acid. Such a solution, for example, may be used to impregnate gauzes at moderate temperatures such as at a temperature of about 40 C. A thus treated gauze may be prepared as described in the preceding example.

Example 4.About 500 grams aluminum hydroxide or clay or glass powder are introduced into about 500 cc. of a boiling solution as given in Example 2 and boiled for about 30 minutes. The thus treated Powder is then flltrated and washed and dried.

Example 5.-A bandage gauze is dipped into 1% AgNOs solution, wrung out, dried and immersed into a cold 20% NaCl solution for one hour, and washed carefully. The gauze does not discolor when exposed to light.

Example 6.A bandage gauze is dipped into 1% AgNOa solution, wrung out, dried and immersed into a cold 5% NaCl solution for 24 hours, and washed carefully. The gauze does not discolor when exposed to light.

Example 7.8 g. silver nitrate are dissolved in 1 liter water which is saturated with calcium chloride. This solution may be used for the sterilization of surgical instruments or for any other purpose for which silver preparations may be eii'ectively used.

Example 8.'! a. silver chloride are dissolved in 1 liter of a concentrated calcium chloride solution. Preferably the silver chloride will be dissolved under the application of heat.

Example 9.-8 grams silver nitrate are dissolved in 1 liter of a concentrated calcium chloride solution containing 1 cc. hydrochloric acid cone,

Example 10.10 g. silver nitrate are dissolved in 1 liter of a concentrated calcium bromide solution.

Example 11.10 g. cotton gauze was boiled for minutes in 10 liter water containing 5% NaCl and .03% AgNOs. The gauze contains about .2-.4% Ag corresponding to about .3-.7% AgNOs.

Example 12.--275 g. cotton duck was boiled for 40 minutes in 10 liter water containing 10% NaCl and .12% AgNOa. The duck contains about 1.7% Ag corresponding to 2.65% AgNOs. The cotton duck accordingly had removed about 7.3 g.

AgNO: and reduced the silver content to about .05% AgNOa. The duck accordingly has absorbed about 20 times more than corresponds to the concentration of the solution retained therein.

one described more in detail in Example 13 of the copending application for improvement in sterilizing compositions and methods for making same. I

As can be seen from Example 8, it may be advantageous to dissolve the silver under the application of heat as it is introduced in the form of a relatively insoluble compound.

This invention is not restricted by any of the above examples but is to be understood in its broad scope as given in the appended claims. The term sterilizing" as used throughout this specification and the appended claims is to be understood as comprising all the various above described actions 01' silver compounds such as their disinfectant, fungicidal, bactericidal, germicidal, and the lik actions. The terms simple silver halide, halide, and "halogeno compounds are to be understood as defined in earlier parts 01' this specification. It also should be understood that wherever solutions are mentioned throughout the specification and the appended claims this expression is not to be limited to aqueous solutions but is meant to comprise other suitable solvents such as alcohol, glycerine, carbon tetrachloride, and the like. As far as silver halide preparations and solutions are concerned, as a rule aqueous solutions will be preferable because 01' their higher solvent and ionization power. In some cases mixed solvents such as diluted alcohol and so forth, may be desirable.

What we claim is: 1. A sterilizing preparation the efl'ective agent of which is a. silver halide preparation which is 36 adsorbed on a carrier and has the general formula Ag.H81.HB.1z.M1 in which formula Hal is a halogen selected from the group consisting of chlorine, bromine and iodine, M is a cation, including hydrogen, which is capable of forming readily soluble halides, 11 is the index of M de- Example 1a-275 g. cotton duck was boiled for 40 minutes in 10 liter water containing 10% NaCl and about .035% AgNOs. The duck contained .2% Ag corresponding to .3% AgNOa. Accordingly the duck had removed about .8 g. AgNOa from the bath thus reducing its content to about .027%. The duck has absorbed about six times more than corresponds to the concentration of the solution. The remaining bath is nearly exhausted. As can be seen by comparison with Example 12, the remaining bath in Example 12 is not exhausted. Reduction of time will result in somewhat proportional decrease of silver adsorption in Example 12.

In the same way one may proceed with other materials such as, e. g., burlap. The treatment according to Examples 11-13 is analogous to the termined by the stoichiometer amount of M capable of combining with H312. and x is a number indicating the excess halogen introduced into the said compound over that required for the formation of the simple silver halide, the upper value of .1: being limited by the amount of halogen which can be introduced without increasing substantially the solubility of the said silver halide preparation over that of the simple silver halide.

2. A silver halide preparation according to claim 1 in which the halide is introduced in the form of a metal halide which is selected from the group consisting of the alkali metal and alkaline earth metal chlorides, bromides and iodides.

3. A sterilizing preparation according to claim 1 in which the carrier on which the silver halide preparation is adsorbed is a cotton material.

4. A sterilizing material according to claim 1 in which the silver halide preparation is formed by a metal M which metal M is a cation capable of forming hygroscopic simple halides.

5. The method of preparing a sterilizing material which consists in treating a material which is adsorbent for silver halide with a solution of a silver compound and of a soluble halide for at least twenty minutes precipitating thereby a silver halide preparation on the said adsorbent material and washing oil. any loosely adherent nonadsorbed silver halide from said adsorbent material, the said halide containing mor halide than corresponds to the simple silver halide, the said halide being selected from the group consisting of chlorine, bromine and iodine.

6. The method 01' preparing a sterilizing material which consists in treating a material which is adsorbent for silver halide with a solution of a silver compound and of a soluble halide at elevated temperature precipitating thereby a silver halide preparation on the said adsorbent material and washing ofi any loosely adherent non-adsorbed silver halide from the said adsorbent material, the said halide containing more halide than corresponds to the simple silver halide, the said halide being selected from the group consisting of chlorine, bromine and iodine.

'7. The method of preparing a sterilizing material which consists of impregnating a material which is adsorbent for silver halide with a silver compound and then treating it with a solution of a water soluble halide for at least twenty minutes and forming thereby a silver halide preparation, the said halide being selected from the group consisting of chlorine, bromine and iodine, and the said solution containing more halide than corresponds to the simple silver halide.

8. The method according to claim '7, which comprises treating the said impregnated material with the said solution of a soluble halide at an elevated temperature.

9. The method according to claim 1 which comprises treating the said impregnated material with the said solution of a halide at an elevated temperature and at a pH of less than 7.

IGNAZ KREIDL. WERNER KREIDL. 

